fix: renderer race condition (#210)

Guard accessing the underlying Termenv output behind a mutex. Multiple goroutines can set/get the dark background color causing a race condition.

Needs: https://github.com/muesli/termenv/pull/146

renderer.go

@@ -2,6 +2,7 @@ package lipgloss
 
 import (
 	"io"
+	"sync"
 
 	"github.com/muesli/termenv"
 )
@@ -16,6 +17,7 @@ var renderer = &Renderer{
 type Renderer struct {
 	output            *termenv.Output
 	hasDarkBackground *bool
+	mtx               sync.RWMutex
 }
 
 // RendererOption is a function that can be used to configure a [Renderer].
@@ -43,11 +45,15 @@ func NewRenderer(w io.Writer, opts ...termenv.OutputOption) *Renderer {
 
 // Output returns the termenv output.
 func (r *Renderer) Output() *termenv.Output {
+	r.mtx.RLock()
+	defer r.mtx.RUnlock()
 	return r.output
 }
 
 // SetOutput sets the termenv output.
 func (r *Renderer) SetOutput(o *termenv.Output) {
+	r.mtx.Lock()
+	defer r.mtx.Unlock()
 	r.output = o
 }
 
@@ -78,6 +84,8 @@ func ColorProfile() termenv.Profile {
 //
 // This function is thread-safe.
 func (r *Renderer) SetColorProfile(p termenv.Profile) {
+	r.mtx.Lock()
+	defer r.mtx.Unlock()
 	r.output.Profile = p
 }
 
@@ -110,6 +118,8 @@ func HasDarkBackground() bool {
 // background. A dark background can either be auto-detected, or set explicitly
 // on the renderer.
 func (r *Renderer) HasDarkBackground() bool {
+	r.mtx.RLock()
+	defer r.mtx.RUnlock()
 	if r.hasDarkBackground != nil {
 		return *r.hasDarkBackground
 	}
@@ -139,5 +149,7 @@ func SetHasDarkBackground(b bool) {
 //
 // This function is thread-safe.
 func (r *Renderer) SetHasDarkBackground(b bool) {
+	r.mtx.Lock()
+	defer r.mtx.Unlock()
 	r.hasDarkBackground = &b
 }

renderer_test.go

@@ -1,6 +1,7 @@
 package lipgloss
 
 import (
+	"io"
 	"os"
 	"testing"
 
@@ -29,7 +30,24 @@ func TestRendererWithOutput(t *testing.T) {
 	defer os.Remove(f.Name())
 	r := NewRenderer(f)
 	r.SetColorProfile(termenv.TrueColor)
-	if r.output.Profile != termenv.TrueColor {
+	if r.ColorProfile() != termenv.TrueColor {
 		t.Error("Expected renderer to use true color")
 	}
 }
+
+func TestRace(t *testing.T) {
+	r := NewRenderer(io.Discard)
+	o := r.Output()
+
+	for i := 0; i < 100; i++ {
+		t.Run("SetColorProfile", func(t *testing.T) {
+			t.Parallel()
+			r.SetHasDarkBackground(false)
+			r.HasDarkBackground()
+			r.SetOutput(o)
+			r.SetColorProfile(termenv.ANSI256)
+			r.SetHasDarkBackground(true)
+			r.Output()
+		})
+	}
+}

style.go

@@ -185,9 +185,10 @@ func (s Style) Render(strs ...string) string {
 	var (
 		str = joinString(strs...)
 
-		te           = s.r.ColorProfile().String()
-		teSpace      = s.r.ColorProfile().String()
-		teWhitespace = s.r.ColorProfile().String()
+		p            = s.r.ColorProfile()
+		te           = p.String()
+		teSpace      = p.String()
+		teWhitespace = p.String()
 
 		bold          = s.getAsBool(boldKey, false)
 		italic        = s.getAsBool(italicKey, false)

style_test.go

@@ -9,8 +9,9 @@ import (
 )
 
 func TestStyleRender(t *testing.T) {
-	renderer.SetColorProfile(termenv.TrueColor)
-	renderer.SetHasDarkBackground(true)
+	r := NewRenderer(io.Discard)
+	r.SetColorProfile(termenv.TrueColor)
+	r.SetHasDarkBackground(true)
 	t.Parallel()
 
 	tt := []struct {
@@ -18,31 +19,31 @@ func TestStyleRender(t *testing.T) {
 		expected string
 	}{
 		{
-			NewStyle().Foreground(Color("#5A56E0")),
+			r.NewStyle().Foreground(Color("#5A56E0")),
 			"\x1b[38;2;89;86;224mhello\x1b[0m",
 		},
 		{
-			NewStyle().Foreground(AdaptiveColor{Light: "#fffe12", Dark: "#5A56E0"}),
+			r.NewStyle().Foreground(AdaptiveColor{Light: "#fffe12", Dark: "#5A56E0"}),
 			"\x1b[38;2;89;86;224mhello\x1b[0m",
 		},
 		{
-			NewStyle().Bold(true),
+			r.NewStyle().Bold(true),
 			"\x1b[1mhello\x1b[0m",
 		},
 		{
-			NewStyle().Italic(true),
+			r.NewStyle().Italic(true),
 			"\x1b[3mhello\x1b[0m",
 		},
 		{
-			NewStyle().Underline(true),
+			r.NewStyle().Underline(true),
 			"\x1b[4;4mh\x1b[0m\x1b[4;4me\x1b[0m\x1b[4;4ml\x1b[0m\x1b[4;4ml\x1b[0m\x1b[4;4mo\x1b[0m",
 		},
 		{
-			NewStyle().Blink(true),
+			r.NewStyle().Blink(true),
 			"\x1b[5mhello\x1b[0m",
 		},
 		{
-			NewStyle().Faint(true),
+			r.NewStyle().Faint(true),
 			"\x1b[2mhello\x1b[0m",
 		},
 	}